The invention concerns a rotary piston adjuster for adjusting the angular position of the camshaft of an internal combustion engine, particularly according to the preamble of claim 1.
The camshaft, and the entire valve train of the internal combustion engine possesses a frictional torque that acts in opposition to its driving torque and tends to shift the rotary piston adjuster in a direction of retard. This intensifies its retarding adjustment and hinders its advancing adjustment and thus leads to different adjusting speeds in advance and retard directions. Further, locking and unlocking of the rotary piston adjuster are influenced by the frictional torque of the camshaft. Due to the retarding adjustment favored by friction, adjusters of the exhaust camshaft that lock in an advance position have a tendency to make the locking element clamp when it is unlocked. The reason for this is that the frictional torque of the camshaft and the oil pressure of the working chamber A required for unlocking, load the locking element prior to unlocking in a direction leading away from the advance stop toward the retard stop and cause it to clamp.
Unlocking in the retard position is uncritical especially if the frictional torque of the camshaft acting in the direction of the retard position is supported on a retard stop that is separated from the locking element so that the locking element is relieved of load.
A known means for equalizing the differing speeds of adjustment and facilitating unlocking in the advance position are compression springs that are arranged in advance adjusting chambers with their torque acting in opposition to the frictional torque of the camshaft.
The generic document DE 197 26 300 A1 discloses a rotary piston adjuster for adjusting the angular position of the camshaft of an internal combustion engine. This adjuster comprises an outer rotor connected to a drive pinion and an inner rotor connected to the camshaft. The outer rotor comprises at least one hydraulic chamber with radial separating walls and the inner rotor possesses at least one pivoting vane that sealingly divides the hydraulic chamber into a working chamber A and a working chamber B and is hydraulically pivotable between a retard stop position and an advance stop position. A locking device enabling a detachable connection of the outer and inner rotors and at least one compression spring acting in opposition to the frictional torque of the camshaft are arranged between the two rotors. These compression springs that are arranged in the advance adjusting chambers at a distance from the inner periphery of the outer rotor are supported only in depressions of the radial separating walls and of the pivoting vanes. In this way, when the outer rotor pivots, a contact between the hard spring steel and the outer rotor and the wear resulting therefrom are avoided. A drawback of this arrangement is a possible instability of the compression spring that restricts its design relative to spring rigidity and length and thus also its potential functions.
The object of the invention is to provide a rotary piston adjuster of the pre-cited type that permits a free design of the compression spring within broad limits and a low-wear operation with this spring.
The invention achieves the above object by implementing the features listed in the body of claim 1. The attachment offers enough room even for a compression spring that is longer than a hydraulic chamber of the rotary piston adjuster. A larger spring length permits a low spring rate that brings about a desired small increase of the spring force over the angle of pivot of the inner rotor. This is particularly important in the case of compression springs whose spring force is so large that they effect a strong support of the rotary piston adjuster on the advance stop and thus render a locking on the advance stop superfluous. The required stabilization of a long compression spring is enabled by the wear-resistant components of the attachment in which the compression spring is supported and guided. A pointwise support of the spring can additionally reduce wear.
Basically, it is also possible to use a flat coil spring that requires no support in place of a compression spring. However, due to its small shape efficiency factor, a flat coil spring with the same spring torque has a larger overall volume than a compression spring.
According to an advantageous feature of the invention, the attachment comprises an intermediate plate having a side washer and a cover as also a disc-shaped bushing that together form an end closure of the outer rotor on its end directed away from the camshaft. The fact that the attachment at the same time constitutes the end closure of the outer rotor leads to a saving of axial design space. The attachment can, however, also be arranged on the camshaft-side end of the outer rotor. In this case, the drive pinion is configured as an intermediate plate comprising a locking device and stops while its end directed away from the camshaft is closed with an additional cover.
For lodging the compression spring in the attachment, it is advantageous if the intermediate plate that is connected to the outer rotor comprises a coaxial bore whose periphery is configured with a circular segment-shaped recess having a radially extending end surface. The length of the circular segment-shaped recess can be chosen to correspond to the desired length of the compression spring.
An advantageous feature of the invention is that the disc-shaped bushing that is connected to the inner rotor is sealingly guided in the coaxial bore of the intermediate plate as well as between the side washer and the cover, and that a peg comprising at least one radially extending side surface is arranged on the outer periphery of the disc-shaped bushing for pivoting within the circular segment-shaped recess. According to another advantageous feature, the compression spring is supported in the circular segment-shaped recess on the radially extending end surface thereof and on the radially extending side surface of the peg and bears against the periphery of the circular segment-shaped recess. In this way, the compression spring is supported over its entire length and its spring torque loads the outer rotor through the intermediate plate and the inner rotor through the disc-shaped bushing.
According to still another advantageous feature of the invention, the cover comprises a groove-shaped indentation that laterally widens the circular segment-shaped recess and thus creates room for accommodating a compression spring having a circular turn cross-section. In this way, the compression spring is also laterally guided and thus achieves maximum shape stability.
If the radial height of the recess and the peg is larger than the turn diameter of the compression spring, this latter can bear not only against the periphery of the recess but, with the help of arc-shaped spacers, it can be installed with a smaller diameter. In this way and by varying the pre-stress of the compression spring, the spring torque can be adjusted. It is also conceivable to arrange two or more compression springs one on top of the other and separate their turns with interposed sheets. It is also imaginable to provide further recesses in the intermediate plate and further pegs for further compression springs connected in parallel. With all these possibilities, the spring torque of the compression spring can be varied within broad limits and adapted to the frictional torque of the camshaft or to a value above or below this.
If the compression spring is pre-bent into an arc shape and thus is already given the desired radius of curvature during fabrication, any additional stresses and radial forces that may arise due to shape deviations during the bending of straight compression springs and would act on the spring supports are avoided.
The groove-shaped indentation of the cover is rendered superfluous by using a different type of compression spring, viz., a compression spring with an oval turn cross-section having the same width as the intermediate plate. However, in this space-saving solution, it is no longer possible to vary the turn diameter of the compression spring.
In an alternative embodiment of the invention, a rotary piston adjuster comprises a lengthened hydraulic chamber in which at least one compression spring is arranged that is supported on a separating wall and on a pivoting vane as also, at least pointwise, on the inner periphery of an outer rotor. In this embodiment, even if a plurality of compression springs are arranged next to one another, no additional axial space is required. However, the outer rotor and the pivoting vane must be wear-resistant. Outside of the range of pivot of the pivoting vane, the inner periphery of the outer rotor can be configured so that contact with the compression spring is only pointwise. In this way, shape deviations of the compression spring that could promote wear no longer have a detrimental effect. If locking is effected by a slidable pivoting vane, this must not be loaded by the compression spring.
An adjusting device with an external stop and a compression spring arranged in one of the hydraulic chambers is also conceivable. Even a variant with an internal stop and a spring mounted externally in an attachment is possible. Irrespective of its arrangement, a compression spring having an appropriate pre-stress and direction of action can replace a locking device (e.g. a locking body or pin or vane). A uniform speed of adjustment of an adjuster with retard locking can likewise be realized both with an external and an internal arrangement of the spring. If there are locking or unlocking problems with an adjusting device that locks in the retard position, the compression spring can be installed so as to act in the retard direction. This gives support to the frictional torque of the camshaft which means that the speeds of adjustment differ even more than before. In this case, too, with an appropriate spring design, a locking device can be dispensed with.
Further features of the invention are disclosed in the claims, in the following description and in the drawings in which examples of embodiment of the invention are schematically represented.